function y = mat2huff(x)
    % MAT2HUFF Huffman encodes a matrix.
    %   Y = MAT2HUFF(X) Huffman encodes matrix X using symbol
    %   probabilities in unit-width histogram bins between X's minimum
    %   and maximum values. The encoded data is returned as a structure
    %   Y: 
    %      Y.code   The Huffman-encoded values of X, stored in
    %               a uint16 vector.  The other fields of Y contain
    %               additional decoding information, including:
    %      Y.min    The minimum value of X plus 32768
    %      Y.size   The size of X
    %      Y.hist   The histogram of X
    %
    %   If X is logical, uint8, uint16, uint32, int8, int16, or double,
    %   with integer values, it can be input directly to MAT2HUFF. The
    %   minimum value of X must be representable as an int16.  
    %
    %   If X is double with non-integer values---for example, an image
    %   with values between 0 and 1---first scale X to an appropriate
    %   integer range before the call. For example, use Y =
    %   MAT2HUFF(255*X) for 256 gray level encoding.   
    %
    %   NOTE: The number of Huffman code words is round(max(X(:))) -
    %   round(min(X(:))) + 1.  You may need to scale input X to generate
    %   codes of reasonable length.  The maximum row or column dimension
    %   of X is 65535. 
    %
    %   See also HUFF2MAT.
    

    if ndims(x) ~= 2 | ~isreal(x) | (~isnumeric(x) & ~islogical(x))
       error('X must be a 2-D real numeric or logical matrix.');
    end
    
    % Store the size of input x.
    y.size = uint32(size(x));
    
    % Find the range of x values and store its minimum value biased
    % by +32768 as a UINT16.
    x = round(double(x));
    xmin = min(x(:));
    xmax = max(x(:));
    pmin = double(int16(xmin));
    pmin = uint16(pmin + 32768);    y.min = pmin;
    
    % Compute the input histogram between xmin and xmax with unit
    % width bins, scale to UINT16, and store.
    x = x(:)';
    h = histc(x, xmin:xmax);
    if max(h) > 65535
        h = 65535 * h / max(h);
    end
    h = uint16(h);   y.hist = h;
    
    % Code the input matrix and store the result.
    map = huffman(double(h));          % Make Huffman code map
    hx = map(x(:) - xmin + 1);         % Map image
    hx = char(hx)';                    % Convert to char array
    hx = hx(:)';
    hx(hx == ' ') = [];                % Remove blanks
    ysize = ceil(length(hx) / 16);     % Compute encoded size
    hx16 = repmat('0', 1, ysize * 16); % Pre-allocate modulo-16 vector
    hx16(1:length(hx)) = hx;           % Make hx modulo-16 in length
    hx16 = reshape(hx16, 16, ysize);   % Reshape to 16-character words
    hx16 = hx16' - '0';                % Convert binary string to decimal
    twos = pow2(15:-1:0);
    y.code = uint16(sum(hx16 .* twos(ones(ysize, 1), :), 2))';

end % ending function